This invention relates to preparing compositions that include a fluoroelastomer and a fluoroplastic.
Fluoroelastomers are elastomers prepared by curing an uncured fluoroelastomer precursor ("gum") made from monomers containing one or more atoms of fluorine, or copolymers of such monomers with other monomers, the fluoromonomer(s) being present in the greatest amount by mass. Fluoroelastomers have been used successfully in a number of applications due to their ability to withstand high temperatures and aggressive chemicals, as well as the ability of the fluoroelastomer gum to be processed using standard elastomer processing equipment. In addition, fluoroelastomers have been used in fuel management systems such as automotive fuel hoses, filler neck hoses, injector o-rings, and the like. Fuel management applications require low fuel vapor permeation in combination with good low temperature properties, sealability, and flexural properties.
Fluoroelastomers with high fluorine content show good fuel permeation resistance. However, high-fluorine content fluoroelastomers such as high-fluorine content terpolymers based on tetrafluoroethylene, vinylidene fluoride, and hexafluoropropylene have some limitations. For example, when the tetrafluoroethylene content (and thus the fluorine content) is high, flexibility and processability tend to be compromised. With respect to processability, the high fluorine content may render a fluoroelastomer too stiff for curative incorporation on standard processing equipment such as roll mills or Banbury mixers, which requires a material with a melting point less than about 100.degree. C. On the other hand, when the hexafluoropropylene content, at the expense of vinylidene fluoride, is too high, both the polymerization rate and the cure rate may become unacceptably slow for commercial production.
Fluoroplastics are uncured plastics based on polymers made with monomers containing one or more atoms of fluorine, or copolymers of such monomers with other monomers, the fluoromonomer(s) being present in the greatest amount by mass. Examples include melt-processable co- and terpolymers based upon tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. Such fluoroplastics have melting points greater than 100.degree. C. and exhibit good resistance to fuel vapor permeation, as well as good low temperature properties, but compromise the flexural properties needed for flexible fuel management applications. For example, in fuel hoses the stiffness of these materials can lead to disadvantages such as wrinkling when the hoses are loaded onto forming mandrels, increased push-on force during hose installation, and sealing concerns at connection points.